Renovating historic buildings can be a thorny problem. The knee-jerk reaction is to treat them a classic pieces of architecture and to restore them almost as a living museums. But conservation principles have evolved. 'The worst that can be done to a heritage building is to add an antique-looking pastiche to it,' says Professor Lee Ho-yin, director of the architectural conservation programme at University of Hong Kong. Lee cites Heritage 1881, a declared monument in Tsim Sha Tsui, as an example of what not to do. The compound and original buildings are protected, but developer Cheung Kong (Holdings) has tacked on to the former Marine Police headquarters a luxury shopping mall and other additions disguised in faux-classical architectural decoration. 'They added a lot of new things, but in a postmodernist historical approach,' Lee says. 'The old and new are just grafted together. It's very problematic because in five years people who aren't trained won't be able to tell the old from the new.' The 'recreation of the past' approach to conservation was championed in the 19th century by Eugene Viollet-le-Duc, who restored Notre Dame in Paris and the fortified town of Carcassonne. But the practice is obsolete - even though it is still common throughout China, Lee notes. Current practice stipulates that 'new work should be readily identifiable as such', a policy laid out in the Burra Charter that governs heritage management in Australia. The wording is echoed by the group English Heritage for its conservation principles in Britain. On a grand scale, I.M.Pei's groundbreaking glass pyramid outside the Louvre Museum in Paris is probably the best example of a new addition that is clearly distinguished from the monument it fronts. Though controversial when it was inaugurated in 1988, it is now recognised as a classic piece of architecture in its own right.